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https://issues.apache.org/jira/browse/PHOENIX-17?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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James Taylor reopened PHOENIX-17:
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Assignee: (was: rajeshbabu)
I'll update the summary of this JIRA, but this would be for global indexes to
support using an index that doesn't cover all the columns. We already do this
for local indexes.
> Support to make use of partial covered indexes in scan
> ------------------------------------------------------
>
> Key: PHOENIX-17
> URL: https://issues.apache.org/jira/browse/PHOENIX-17
> Project: Phoenix
> Issue Type: Improvement
> Reporter: rajeshbabu
>
> Normally when we want to use secondary indices we create index on one or very
> few
> columns of interest in query conditions. Index may not contain all the
> columns to retrieve.
> Currently Phoenix supporting full covered indexes only(where all or most of
> the columns
> should be in the index in many cases). When we run a query we will choose to
> scan from user table
> or index table based on condition that whether all projected columns in the
> index or not.
> This approach may have some disadvantages mainly in case of wider tables.
> 1)If we did just store all the columns in the index, then it would be just
> like creating another copy of the entire table
> – which would take up way too much space and would be very inefficient for
> wider tables.
> 2) Some times if user creates index on few columns and observes that index is
> not getting used
> and then he need to add all the projected columns to index(may be to the part
> of index or included columns).
> which is something like we are exposing design decisions to the users,
> especially when we already
> target to simplify user's experience by giving SQL on top of a noSQL DB.
> 3) One more thing is as of now if we have an index table contains all
> projected columns in the
> query then we are simply scanning index table only.This can also become full
> table scan when we don't
> have any condition in the query or condition on non primary key column of
> index.
> Some times this might give bad performance than normal table full scan.
> This JIRA is to support making use of partial covered indexes to avoid full
> table scan.
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